1. Field of the Invention
The present invention relates to an illumination apparatus which has a high condensing performance and realizes a high luminance and a reduction in size, and an image capturing apparatus and a projector apparatus using this illumination apparatus.
2. Description of the Related Art
As a condensing illumination apparatus which efficiently illuminates a specific position, there are, e.g., a care headlight, a stand illumination, a spot light, a flashlight, an illumination unit for a data projector and others. A conventional condensing illumination apparatus is usually intended to perform illumination with a high condensing performance by a relatively simple method. That is, light from a light emission source relatively closer to a point light source is reflected by a reflection unit with an ingenious reflection shape. Further, the reflected light is condensed on an optical lens or the like. The directivity of light rays is thus enhanced.
Although this can be also applied to general illumination, a demand for acquisition of brighter illumination light without increasing sizes of apparatuses is high in these condensing illumination apparatuses. In general, however, although the size of a light emission source is increased in order to obtain brighter illumination light, applied power of the light emission source is increased to enhance output. Furthermore, at the same time, a reflection unit or an optical lens which is relatively enlarged with respect to a light emission source is applied in order to increase the condensing performance. Therefore, the size of the illumination apparatus is necessarily increased with respect to the light emission source in order to obtain the brightness with the excellent condensing efficiency. In other words, provision of a small light emission source which has a high output and approximates a point light source enables a reduction in size of the entire illumination apparatus. Based on such a demand, a reduction in size of the light emission source has been advanced even in a conventional mode, and a small light emission source which is of a discharge type enabling a high output is current key means. However, even in case of a small discharge type light emission source, there are many problems with respect to a reduction in size as an entire illumination apparatus. For example, driving by a high-voltage power source whose circuit scale is hard to be reduced is required. In regard to a reduction in size of the illumination apparatus using a small discharge type light emission source, it is said that such a reduction has substantially got close to its limit.
In contrast, as a small light emission source for coming generation, a light emitting diode (which will be abbreviated as an LED hereinafter) has attracted the considerable attention. When it comes to the LED, although it has advantages such as a small size, high-resistance characteristics, a long duration of life and others, it has a limit in its light emission efficiency and a light emission output. Therefore, the LED has been mainly applied as an indicator illumination for various kinds of measuring gauges or a control state confirmation lamp. In recent years, however, the light emission efficiency has been rapidly improved. It is said that it is a matter of time before exceeding the light emission efficiency of a discharge type high pressure mercury lamp or a fluorescent lamp which is conventionally considered that it has the highest efficiency. With emergence of this high-efficiency high-luminance LED, a high-output light emission source using the LED has rapidly serves practical use. Moreover, in recent years, the fact that a blue LED as well as conventional red and green LEDs has advanced to the practical stage accelerates its application. In fact, using the plurality of high-efficiency high-luminance LEDs has started practical applications to traffic lights, an outdoor type large full-color display, various kinds of lamps for a vehicle and a backlight of a liquid crystal display in a mobile phone which are conventionally impossible due to the brightness or the efficiency.
As a promising small light emission source of an illumination apparatus in which the condensing performance is demanded, an application of this high-efficiency high-luminance LED has been considered. The LED basically has characteristics superior to other light emission sources in a life duration, the durability, a lighting speed and the simplicity of a lighting drive circuit. Additionally, the fact that blue is added and three primary colors are provided for the light emission source of spontaneous light has enlarged an application range as a full-color image display apparatus. As a typical example of an illumination apparatus in which the condensing performance is demanded, there is, e.g., a projector display apparatus which forms a display image from image data and projects this image. This projector display apparatus conventionally separates a desired primary color from light from a white color type light emission source by using a color filter or the like, performs spatial light modulation with respect to image data corresponding to each color and spatially or temporally combines the modulated data, thereby enabling color image display. When a white color type light emission source is used, since a desired one color is separated and utilized, it is often the case that other colors than the separated color are uselessly wasted. However, the LED emits light of a desired color itself, it can emit a necessary quantity of light when the need arises. Therefore, light of the light emission source can be efficiently utilized without wasting the light as compared with the conventional white color type light emission source.
Paying notice to excellent application conditions of such an LED, examples in which the LED is applied in an illumination apparatus for a projector display apparatus are disclosed in, e.g., Jpn. Pat. Applin. KOKAI Publication No. 11-32278, U.S. Pat. No. 6,227,669 B1 and others. In the technique disclosed in these publications, a light quantity is assured by constituting a plurality of LEDs. Further, light beams from individual light emission sources are partially condensed by an optical element such as an optical lens, and a light modulation element to be irradiated performs a light beam control in such a manner that these light beams can be successfully set within an allowed incident angle. In general, a widely used light modulation element such as a liquid crystal device has a very small incident angle allowed as illumination light. It is, therefore, ideal to not only provide the simple condensing performance but also form light beams with the higher parallelism and use them for irradiation. This is a very important point when increasing the light utilization efficiency in the light modulation element.